You learn to fuse two spells into a single higher-level spell.
Prerequisites
Ability to spontaneously cast spells.
Benefit
By sacrificing two spell slots of the same level, you are able to cast a single spell you know that is one spell level higher. For instance, you could sacrifice two 1st-level spells to cast a single 2nd-level spell you know or to apply a +1 metamagic feat to a 1st-level spell you know.